Vacuum Advance - Ported vs Manifold: Which to Use & When !!!

[@ThunderHead289]

were you guys able to follow along with this? what didn't maker sense? id be happy to answer your questions below - there is a lot involved here, and it can be difficult to grasp. Check out my friend Ted's distributors - ill be running one on my supercharged 5.0 build! progressionignition.com/

[@poijupoij]

Good video. I thought you were going to point out the actual hose connection points on each type of carb when you had them displayed.

[@BillyTpower]

cool, very good vid for an old dog like me, turns out you can teach us new tricks haha. Quick question about your buddies new distributor design, i see an electronic board in there, so would that not get fucked by water more so than stock Luke?

[@ddgatewood71]

@@BillyTpower I haven't seen that one personally but I'm willing to bet it's PCB is either conformally coated or the distributor cap is sealed. It could be potted, too, or that pic was for display. I'm going to grab one soon so I'll let ya know

[@Paulman50]

That was one of the best explanations I've heard on the subject.

[@chrisebert7307]

I agree about it being a great explanation. Best way I have ever seen it explained. Thank you

[@CarminesRCTipsandTricks]

Thank God SOMEONE under the age of 40 actually understands this!! Gives me some hope for the future.

[@ChuckoMountain-fv9yj]

Im near 80, and did it all back in the day......

[@edsel1952]

I am 62 years old and well versed on carburetors and their circuits. You are spot on with your description and you are so articulate in your explanation of what is going on in the combustion process. I am lucky enough to have spanned both the carbureted engine era and the electronic fuel injection transformation that I understand both. I so respect you and your in-depth knowledge of carburetors and hope you can pass this on to the younger people. I remember the ignorance of my youth before I understood the simple yet sometimes complexity of carburetion. Thanks for the videos.

[@ThunderHead289]

Man that means a lot - I was jaded from the beginning against the modern stuff because my dad taught me with carbs - just so easy to get around an engine bay, once I experienced that, there was no going back!

[@markconrad4160]

Man,I wish I had you as my nabor.i put in a carbed 351w engine in my f150, and it's running rough. Many shops don't even want to touch a carbed engine.

[@ShaunPrince]

I can definitely relate. I am only 42, but I have spent so many summers just trying to tun my carburator, just to have it run terrible in the Canadian winter. Now I just use my vacuum gauge to fine tune my carburator and timing to the changing seasons. I actually love the task, as it give me the opportunity to constantly go over all of the other systems at the same time.

[@chuckthebull]

I'm 65 and have a 1962 sunbeam alpine with an inline 4 and dual carbs I have tuned like a Swiss watch.. But I love this guys work and knowledge... Might think about it for my 1973 lemans.

[@DumbCarGuy]

Dude, now your 65

[@roberthemphill8588]

Luke, enjoyed the video. Good to see a young man have such in depth knowledge of old time carb operation.

[@chickensfloat7427]

Most dont care to learn when us young folk are given shit for getting any lil thing wrong 🤣

[@chickensfloat7427]

@@b_ouncedatazz folk

[@chrisroach4164]

As a recent new owner of a Chevy 235 straight 6, I discovered the advance diaphragm was shot. I replaced it, and it made a big difference in how the car drives. Engine has dual carbs, dual exhaust. Ported vacuum, just like the single original from the 1950's. One thing your video made clear to me though was that at partial throttle, the vacuum is the same, whether from manifold or above throttle plate. I was concerned that my ported connection was not taking advantage of ignition advance with light load cruising, but now I know. EXCELLENT VIDEO!

[@davestarr7112]

I'm glad I read through the comments before I spouted off, Chris. You took the words right out of my mouth. Massive ditto on your comment, I've probably watched a dozen videos on this subject, but this is the first one that ever bothered to simply hook up two vacuum gauges that show exactly what jaw-jacking is all about. Excellent work here, thanks to Luke.

[@larryfisher3683]

Using manifold vacuum will give you a smoother idle and use less fuel when idling because with the low fuel/air volume in the cylinders the earlier spark advance makes the engine more efficient. The idle speed will then increase using manifold vacuum and adjusting the idle speed down will reduce the fuel consumption and result in a smoother engine that also generates less heat so will run cooler when at idle in traffic. This will be true with a mild or stock cam. At throttle applications above idle both manifold and ported vacuum will be identical as you pointed out in the video.

[@Jgarage5]

good to know! So that's why all my carb adjustment were maxed out on an old 1985 c10 I bought. The timing was so jacked and the TV cable wasn't even hooked up! It was so messed up man, I'm tearing it all down and starting over.

[@undercarview]

This is exactly where I ended up with my engine, switched to manifold vacuum and had to wind 3/4 out of the idle screw to get the idle back down where it was, and it idles smoother now

[@bradgriffith4231]

@Hulagan 808 Actually, most performance engines/heads today will make best power with 32-36 ini / mech advance & the mechanical should be all in by 2400 or so, with today's pump gas, & 32* works better than 36* in most applications, unless one is running ignorant compression & cam duration / overlap. Maybe more timing with a low compression stock motor.

[@8literbeater]

Yes this. This is the truth. Ported vacuum was designed to use more gas and run worse. That was the intent. It causes later ignition so that more fire goes out the exhaust valve and heats up the exhaust to keep the catalytic converter hot. That is all. You're basically burning gas to run an exhaust heater.

[@jeffkellner1585]

@@bradgriffith4231 ttyyy

[@davec9244]

watched this before. For a young guy he haves a lot of knowledge of Carb. and tuning. A dead or dying technology! thank you Luke! stay safe

[@kornami8678]

I completely agree. Plus I always utilized a manifold vacuum gauge with my gauge group. It's a great way to be informed on how the engine is running. It's a gauge that most gear heads are ignorant of.

[@billcat1840]

Great tune aid. I swear by them.

[@jfv65]

In the early 1980's they put them in guage clusters and called them 'econometer'. Old BMW's had them under the speedometer swinging L to R as you stabbed the throttle.

[@DylanMcCoolVideo]

To give an example for cylinder pressure in relation to how much advance timing you need, this example really helped me understand it. Think of two fields full of hay. One field is sparse, and has patches of growth that aren’t close to each other. The other field is dense and has hay all over. Light a match on the fields at the same time, and your dense field is going to burn way faster than the sparse field because the hay is packed tightly together, which means the fire doesn’t have to jump so far to ignite elsewhere. That’s the same way for cylinder pressure. More fuel and air being crammed into the cylinder under load means higher cylinder pressure, which means you need less advance timing to burn at the same rate as you would with the lower cylinder pressures aka the sparse field. If you wanted both fields to be completely burnt at the same time, you would need to light a match on the sparse field earlier than you would the dense field, which translates to needing additional vacuum advance at part throttle cruising. Hope this helps!

[@BillyTpower]

Good explanation Dylan, accept one thing, I am gonna need to bail that hay and if you burn it, i"ll have to come find you,,,, lol haha

[@jhutch1470]

@@BillyTpower Oh crap. Please don't look outside. I tried the experiment and you won't like the looks of your fields. Sorry. LOL

[@Archermboi]

Dylan McCool great explanation

[@neilwhitmore]

so what your saying here is that I should hook my vacuum advance up on my 318, and that I'm losing power because it is not hooked up?

[@billcat1840]

Dont forget cylinder head design affects the burn rate and timing requirements. Low compression and high compression need different curves. My old Pontiacs liked 12 to 14 initial and the total in by 4800...34 to 36 total. 15 inch VA. This was an open chamber head with 8.5:1 comp. A fast burn closed chamber head would completely change the timing needs.

[@jamesmartin2339]

Leaner fuel mixtures = more advance. Aka idle and cruising on the highway. Wide open throttle = no vacuum and no vacuum advance. Ported vacuum = no vacuum at idle. Manifold vacuum = vacuum at idle. Idle timing = what you set with a timing light. If you connect to manifold vacuum you add the advance of your vacuum canister to your idle timing. Depending on vacuum canister usually 10-15 degrees of extra timing. So you can have a reasonable ~10 degrees of timing without kicking back your starter and get the extra timing you need after your engine starts to make vacuum (running). A lot of vacuum cannisters can be adjusted to add or remove timing and you can get them in different varieties based on how much vacuum your engine makes at idle. Engines typically run cooler with the additional advance at idle. The purpose of ported vacuum was an emissions device to purposly heat up your exhaust and reduce emissions. The progression ignition product is basically EFI without fuel control. It gives you a programmable ignition table using a map (vacuum) sensor. This is like the Ford and Chevy fuel injection systems of the 80s without fuel control or a carbureted LS engine with an ignition controller.

[@ThunderHead289]

I agree with everything except the old “it’s for emissions” lies - flatheads before the time of folks caring about emissions or economy utilized a ported vacuum port. You can find it in service manuals. And an engine shouldn’t run hot at idle unless the cooling system is compromised - they aren’t making enough cylinder pressures at idle for them to be that sensitive. Iv actually seen folks run hotter on manifolds because it will favor a lean mixture. Lean doesn’t have as much of a cooling effect and temps will increase. But my biggest reason for running ported is that you can run more aggressive initial mechanical - so when you punch the gas from a stop, you have a much more reasonable advance degree that will help the vehicle get off the line!

[@jamesmartin2339]

@@ThunderHead289 The whole emissions thing was just something I read it might have something to do with EGT (exhaust gas temp) for emissions but you would probably have to talk to a Dyno operator who has seen lots of hard data. If you set your idle mechanical timing to let's say 20 degrees as an example w/zero vacuum advance. You take the same engine and set it to 10 degrees mechanical w/10 degrees of vacuum advance. In both situations you would have the same ignition timing at idle. Springs and bushings are used to set up what rpm you have max power and how quickly you get there. The vacuum advance is used modify your timing for cruise and idle. It adds to your mechanical timing.

[@Kenjh71]

@@ThunderHead289 what if we turn the topic around a bit? Is it improving emissions to run higher exhaust temp, yes or no? Is ported vacuum a means to get higher exhaust temps, yes or no?

[@tinkerjeeppublications9823]

Excellent video. A very clear description of what both vacuum sources do. Essentially the same above scant throttle opening. In my Jeep J20/10 I run a manual vacuum switch. Engine is a 1979 AMC 360 with 8.23:1 CR, Thorley Tri-Y headers, Dual 2.5" pipes, Summit racing mufflers. I tuned an old ACDelco AMC points distributor and am running the stock 1970 360 curve, I think 5* initial advance at 600RPM. The intake side is an Edelbrock Performer manifold topped with an Edelbrock 1405 carb. Unknown cam - it was swapped in years before I got the engine. It is old - likely has 100k miles on it. No idea what upper advance curve is. I don't race it, I just like scootin' around town in it. I run Manifold Vacuum Advance in the cold and switch to Ported when the engine warms up, because, yeah...it idles way jittery warmed up with manifold sourced advance. One thing: I would try this - I noticed your open element air filter on your 289. Try running a closed intake airbox with snorkles running from the front of the vehicle and see if you get any added performance out of the engine. I used to run open filters and I realized the engine was sucking 200 degree engine compartment air. I run dual snorkles on stuff now in hot weather and remove the hoses in the winters...because the temperatures changes from high 90 degrees in the summer to -20 in the winter. And I found out ramming freezing air into an engine is no good. And sucking 200* air is bad in the summer.

[@glenwaldrop8166]

That 200* air is good for fuel economy, hurts power though. Essentially it's like losing a few cubic inches displacement.

[@tinkerjeeppublications9823]

@@glenwaldrop8166 explain the scientific principal of that statement please.

[@glenwaldrop8166]

@@tinkerjeeppublications9823 hotter air is less dense, essentially it's taking in less air for the same throttle position and RPM vs colder air. The heat also helps vaporize the fuel before ignition. There's certainly a temperature cut off point where you lose power and economy but around 200*F under hood temps with an open cleaner is pretty efficient, though slightly down on power. That's partially why older engines had exhaust/coolant crossovers in the intake, to help increase the temp of the intake and the incoming air and increase efficiency. In those cases I'm pretty sure they went too far, most people saw gains by going to a cooler running aluminum intake.

[@billcat1840]

We used timing tape and altered weights and springs to alter timing. Total timing equals initial plus centrifugal and vacuum advance. Some older vacuum advances were adjustable. Different engine combos used different vacuum rates. We used to swap vacuum cans around to change timing. Old school tuning

[@RaysLaughsAndLyrics]

The brain is mightier than the Web. The age of slide rules and pocket protectors will never be equaled.

[@ford351cleveland]

This is why i watch your channel. Super helpful, entertaining and you listen to your viewers thanks a lot man

[@ThunderHead289]

I’m just an average joe - ultimately I just want folks to enjoy their rides and give them the info I wish I had when I was learning. I spent a lot of time being frustrated vs enjoying my classics in the early years!

[@ford351cleveland]

@@ThunderHead289 thanks for sharing your information it really helped me enjoy my 72 Ford i struggled alot with my carb and timing issues because i did not know better and in my country there are not a lot of people with experience. You are one of the main reason why i can enjoy my Sunday rides i do not have to worry about any carb related issue Thanks again and keep up the awesome work i hope one day you can make a career out of this channel and do it full time

[@gsfbffxpdhhdf7043]

Uncle tony garage is better

[@ford351cleveland]

@@gsfbffxpdhhdf7043 Hi man i think they are both awesome channels i just think That Luke goes a little more i detail and responds more to questions then Uncle Tony.

[@SealofPerfection]

Ported vacuum was invented for emissions. If your engine is tuned correctly and you don't have to worry about having all the emissions crap in place, you want manifold. It cannot be beat for performance, driveability, cooling at idle and economy. You can always (and should) have quicker mechanical advance to compensate for the drop in vacuum when you crack the throttle open. There is a huge write up...really, THE definitive write up on ported vs manifold by a former GM engineer that's easily found...originally on Corvette forum, it's been copied to pretty much every auto forum there is. The money shot of his explanation is at the end, though: "For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it - they don’t understand it, they're on commission, and they want to sell "race car" parts." All that aside, that distributor looks pretty cool

[@michaelbenardo5695]

Not so. Most, not all but most, factory setups used ported vacuum even before emissions controls were invented. Certain engines, such as Buick Nailheads, respond great with manifold vacuum, but some don't, such as AMC 6 cyl. They will hesitate and spit back.

[@PaulCTownsend]

Your information is spot on I learned it back in 1979 at Columbia basin college Pasco Washington had a great tune-up electrical instructor Jay Frechette still good friends today. I'm 67 years old. You also might want to explain if you have an automatic transmission that has a vacuum modulator it better be hooked at manifold vacuum at a centralized location on the intake or carb. And that vacuum better drop to zero when you put the throttle to the floor low vacuum = high pressure high vacuum= low pressure. Thanks for the great videos and information.

[@WW226]

This is a topic where it's best to obtain all the knowledge u can and go out and play with it. And go with what the engine likes best. I personally use manifold vacuum. I have a very low vacuum signal at idle (6in) in gear. 14° stop bushing, and 22° initial timing.

[@ThunderHead289]

Yep, and that’s where I tried to add that big cams need more timing - street engines with stock or mild cams will favor ported where big cams that bleed off a lot of compression at idle will need more timing because cylinder pressure is low!

[@taylorsrus9543]

You should ditch the vacuum advance all together.

[@mickangio16]

You said it- "go with what the engine likes best". If your engine only pulls 6" of vacuum at idle speed then I would think that performance is priority and fuel mileage not as important to you. In that case you probably have very light centrifugal advance spring(s) to get full advance quickly. In that situation I am more concerned with having cap/rotor indexed properly than having a functional vacuum advance.

[@nikkerton]

I'm at a place with my '52 Pontiac build on my 350 motor swap using an Edelbrock AVS carb that I'm trying to dial all this in. I've watched many a video and this is the best one yet. Thanks for showing the ported vs manifold vacuum on the road in real time. Also, the weights moving under vacuum on the distributer. It's all dial dial dial it in but this helped me understand this topic just that much more.

[@CrazyPetez]

I like your video. Ported vs. Manifold is certainly a controversial subject. The SBC in my Corvette has a mild performance cam, a 600 cfm Holley DP, and a distributor dialed in by an expert on an old style cam machine, using my engine specs. The engine loves❤️full vacuum to the distributor at idle. Vacuum and base timing are set to a maximum of 36 degrees with 10 degrees initial. It works well, and that’s what counts.

[@Milner62]

All chevrolets love manifold vacuum. It's something you have to do with them to get a smooth idle. Others like fords its hit and miss. I've had some that loved ported and some that loved manifold. I have one that loves both as it runs on manifold and venturi vacuum.

[@CrazyPetez]

Milner62 Thanks for clearing that up. Corvette Forum guys and I stand by manifold vacuum, while other sources claim ported is better. In the end, whichever works best for a particular engine is best for that engine, so experiment.

[@briang4470]

I swear that 99% of old cars I pop the hood on usually have the vacuum advance hooked up to manifold vacuum and it drives me nuts and I have set engines up for people where I wont hook up vacuum advance or I hook it up to ported and when I see the car again, someone usually comes along and hooks it up wrong, and I dont like hooking it up on a engine with a large cam because the vacuum signal will be very weak and on a hotrod u dont need vacuum advance, I personally dont use them to reduce the chances of inconsistent timing because I like to run my timing right on the edge for best performance. Great video man, I really appreciate u taking the time to try to educate folks about ignition timing, it took me a long time to grasp the concept of it and I still dont know everything but u learn best by trial and error.

[@jrbird7571]

Good video. I used to set my initial timing and thought I was done. It makes a difference understanding all of the components and how they work best with your engine. My Pontiac 400 loves a total timing of 36. That's inital + mechanical (no vacuum). Initial is best at 16 for good cranking, so I got a timing curve kit for my distributor to give me 20 mechanical and the springs dictate when it's at full mecahnical which was 2500 RPM. It also doesn't like any additional timing at idle, so I use ported vacuum on the vacuum advance can. The vacuum advance is also adjustable for part throttle cruising. Too much and it's surgey. I have around 10 degrees of vacuum dialed in.

[@ThunderHead289]

That’s science 👆

[@mickangio16]

You didn't mention whether you had an automatic or manual trans but I would like to state that I do not like using manifold vacuum with an automatic trans because when you put the vehicle in gear the rpm drops lowering vacuum and retarding timing causing a crummy idle, makes engine run hotter, and probably increases likelihood of plugs fouling. So, for an automatic transmission vehicle I prefer ported vacuum but also modify the amount of advance in the distributor just as you did (20 degrees) to get the desired timing at idle speed. Manifold vacuum source can work very nicely for manual trans, though.

[@jrbird7571]

@@mickangio16 I have a manual transmission, so at idle my timing sits at 16 with the ported vacuum.

[@sabledriver]

My 84 Capri RS 5.0 4V has a combination where, it has full manifold vacuum when the engine is cold, then switches to ported when warm. This is done with a temperature actuated vacuum tee in the back water passage. I had this removed for some time until I understood the benefit of the extra timing when the engine is cold. Thanks for the informative video.

[@ThePaulv12]

Very good! Re ported vacuum: A great test for any motor and its state of tune, or otherwise, is to pull the vac hose off the vac advance at idle. If it drops in rpm the whole tune of the car is almost always wrong. Also, if the rpm drops every aspect of engine tuning can need adjusting. Initial timing, throttle stop screw, idle mixture and dwell if it has points. Sometimes the tune is so far out it is hard to get a motor to even idle so you can adjust the initial. I marvel that people would argue about such a thing. It indicates an utter lack of understanding of basic mechanical principals. Talk about making something simple complex. No doubt some will still argue because they have SFB! Unless there are some very specific reasons (I can hardly think of one on a street engine and a race engine doesn't usually have vac advance), as the vid says, *a street motor's vac advance should not be plumbed to intake manifold vacuum* This means the port on the carb has to have NO vac at idle - don't plug it onto a vac port that sucks at idle. Also if the throttle stop screw - as mentioned in this *fine vid* - is screwed in too far, the dist port will be opened to manifold vac. This is an accurate vid. Every aspect of it is correct. *No need to challenge* Signed: A mechanic.

[@pattreadwell6149]

Thanks

[@Milner62]

And many hotrodders and real world experimenters will argue because manifold vacuum for vacuum advance is used in some cases. My emission 302 is manifold vacuum. Run ported and nothing you do will get a smooth idle. SBC's love manifold vacuum for advance as well. What you have to remember is under no load or low load situations you run more advance and you run less advance at higher loads. Idling is low load and no one can argue that. Just like vacuum, ported or manifold vacuum is the same only difference is when it comes in. Manifold vacuum is there all the time at idle or part throttle. Ported is only there at part throttle. The amount of vacuum doesnt change though. I myself am going fuel injection on my 306 build for my truck and will be using the timed ignition port. If I dont like it I will switch my timing back to manifold vacuum.

[@philgrossman5381]

@@Milner62 ported vacuum is for smog motors to help pass emissions tests. manifold vacuum is for hot rods.

[@rattle-can-resto5893]

You need more training, go back to UTI and pay attention this time.

[@Milner62]

@@philgrossman5381, not true. Most engines from factory use manifold vacuum. Ported was only used in rare cases and it wasnt for emission reasons. Manifold vacuum will give you a smoother idle as it advances your timing at idle. Ported vacuum is only used when you cant run more advance at idle. Some claim that ported gives you better economy but ported vacuum and manifold vacuum are the same vacuum just when it comes into play. Both manifold and ported vacuum will drop to 0 when you nail the throttle. I prefer manifold vacuum not because it's a "hotrod" thing but because in low load conditions you can run more advance and idling is a low load condition.

[@Fractal_CZ]

Just watched it and told myself:”If only there is something smart to this mechanical solution”. And voi la, Progression Ignition solution. Magic!

[@DJrainbizzles]

Just got my first project car safe to drive and it runs like crap. Turns out I have the timing set up all wrong. Super informative video, now I know what I gotta do tomorrow thanks

[@dr.donscience4518]

Absolutely correct. The biggest problem is that the off-the-shelf distributors have too much mechanical advance for ported vacuum. I had DUI build me a distributor with 12 degrees mechanical advance and a 14 degree vacuum canister. I start with 24 degrees initial timing which using ported vacuum is your idle timing. But I vary that from about 22-26 degrees as needed. So this gives me 24 degrees at idle, 36 degrees total timing and 50 degrees light load cruise which is exactly what a first generation SBC wants. My engines all run perfect. My engines are just street better-than-stock engines with about 32-36 degrees overlap for 350. All my engines have 22” Hg vacuum and idle perfect using a Summit 600 with annular boosters.

[@sewing1243]

I wish there had been KZbin back when I played with "hot" cars. There was so much info that I didn't have access to then that would have helped me make my cars work better.

[@stuartcookie133]

5:40 Very Informative...Also would like to thank you for the patronage....American Hose Clamp and Flat Washer Co.

[@owenjohns6301]

Thanks for taking the time to make this video, it's good info. Personally I like using manifold vacuum so the engine keeps the vacuum advance under deceleration

[@ThunderHead289]

Now that is the one thing I will give you that is indeed better since the mixture goes lean - that’s what I really like about that progression unit!

[@markcole6475]

I like to set base timing on a mod motor as high as it’ll go so it still starts good hot …..then recurve the advance to the desired max! Many times taking out 10 degrees or more from the advance to give it to the base timing. Much better throttle response and power through the whole rpm band! Obviously the carb sometimes needs to be retuned also.

[@jakefriesenjake]

My car runs pretty great right now, but what would you recommend for timing? It's a 381 stroker, aluminum Victor Jr heads, 9.5 to 1, 650 demon carb, the "big mutha thumper" hydrolic roller comp cam, 4 speed manual, 5" of vacuum at idle, 511hp at 6100 rpm. The timing now is 22 and 36 total, with an msd pro Billet On the dyno it still made power at 40 total, but that was with 9.8 to 1, and a race solid roller. What do yo think?

[@markcole6475]

@@jakefriesenjake that seems pretty close imo! I usually run about 10-15 degrees advance in many of my big cammed engines! Really depends on the efficiency of the combustion chamber and rpm range……playing with the timing on a dyno would yield best hp and torque

[@jakefriesenjake]

@@markcole6475 ok thanks!

[@dachine86]

You forgot about the old school cto switches. They would tap into a coolant passage usually in the intake manifold and were supplied with manifold vacuum. It would switch between manifold and ported vacuum output depending on engine temperature.

[@ThunderHead289]

It would advance timing when cold because the mixture is lean - a lean less dense mixture burns slower and requires more timing to burn at the right time 👍 I avoid all that stuff - My montra is “less to fail”

[@SArtisto1]

Chasing Vacuum gremlins on my 79 T-Bird. It has a 351m. I'm still learning the ways of the Carb and these videos are a great help! I had no vacuum at idle and at part throttle to my distributor. I switched to Manifold Vacuum and it "woke" the engine up, tho I had to tweak the vacuum advance can to prevent pinging. I wanted to get better idle economy driving in city traffic which it did, and it fixed the temperature rising issue that I had. I rarely get on the gas, preferring to cruise with light throttle. Its very confusing hearing manifold vs ported vacuum and I'm always wondering if there's a Better way to tune my car

[@Dr_Reason]

One possible issue. If you have an emission tuned motor they used ported vacuum and a lot of degrees of vacuum advance so that they can have decent cruise advance and late timing under low RPM load to reduce NoX pollution. You need to make sure your vacuum can does not add a lot of advance or you will get surging with a proper centrifugal advance curve because the vacuum can is too aggressive for a normal performance setup. Anything after 1970 is suspect. I used to block the travel by drilling a hole in the are at a specific location and putting a machine screw and nut that hit the housing and block out some of the advance.

[@ThunderHead289]

Even most aftermarket units run about 15 degrees. It’s frustrating - there are actually two methods I use which what you stated above is exactly why I tell people ported, because with more initial mechanical, a guy can run a broader advance curve which most units have anyway. The other method is manifold vacuum where your mechanical initial is low, but you use aggressive advance springs BUT when you do that and your vacuum canister brings in another 15, you have WAY too much timing. A lot of old street rodder mod stuff guys used to do to original equipment to make it do what they want - love stories like that.

[@jojomama4787]

Think there's some good info here.I'm a big believer in a vacuum advance as I,along with most people,don't spend a lot of time at high RPMs in daily driving.A more responsive engine and better fuel mileage is what I like.Thanks for helping point things out in a way folks can deal with!

[@Ltmonte]

Vacuum advance isn't related to WOT operation. However, getting it tuned right for either manifold or ported is crucial for part throttle.

[@jayward2662]

I did the t18 swap the first one was aluminum housing found in the bone yard reverse was over and up tore it up (wished I kept) junk it found t18 cast steel back and shoulder destroyed. Lol tried my damnest to destroy it after seven years the rear end come apart. This was in a 75 f1oo or 150 302. The 302 thought it was a 390 and this was back in 88 when I bought it for 600 bucks. Good video my blue oval friend. Carry-on my good sir.

[@crankychicken1151]

You are right seen on the dyno with idle quality and exhaust temps and idle vacuum both ways from mild to wild street engines at Grant Springer. In euguene or

[@ThunderHead289]

Someday, I’d like to have some access to a dyno!!!

[@keithiverson6687]

Good video on this. One of the dangers of running manifold vacuum with too much advanced initial timing on a stock type cam is breaking the nose of the starter off at startup.

[@ThunderHead289]

The biggest problem with running manifold is that you have to have a lazy mechanical initial setting to not have too much timing all together - no problem, utilize quick advance springs to compensate! Well, then you have too much timing while cruising at mid rpm driving rangers 1500-2800 rpm.

[@Milner62]

@@ThunderHead289, you are still limited by initial advance unless you dont mind letting your engine cool off before restarting. As I said on the last video my 302 would not run smooth at idle with ported. Already at 12* initial as I bumped it up for more power. 14* has starter drag when hot. Vacuum advance is really something you shouldnt worry about when it comes in cause vacuum advance is only used for low load conditions any time you hit the throttle hard under load you are running off mechanical advance only till the load lightens and then vacuum advance comes back into play. I'm still trying to grasp how ported vacuum gives you better power and better economy. When you make more power you consume more fuel. It also goes against what ford did for economy by advancing ignition through manifold vacuum stupidly high through the economy calibrated DSII modules. My 78 mercury has one and my manifold vacuum advance 351W with 14* initial with the DSII economy valve to manifold vacuum puts my ignition in the 40* range at idle. Engine made great power and still was able to get me nearly 27 mpg on the highway at 75 mph.

[@softenerguy]

This video made complete sense, and the vacuum gauges helped paint the picture in peoples minds. I take pride in my car starting and running great and my buddies (who I tried to give some tips to) are too stubborn to change their old school bad habits. I'd like to know what parts of this tuning stays consistent and what changes when you start to run bigger cams. Always enjoy, thanks Luke!

[@ThunderHead289]

I’m so glad it made sense - there were some solid suggestions in the comments - driving with the distributor in the cab reed in would have been a very good visual.

[@hotrodray6802]

Yes, if you had a distributor in the cab hooked up in parallel, watching it move would have been neat

[@daver9024]

Excellent explanation of how your vacuum advance works. As you know the factory never did use manifold vacuum , always ported. But lets start backwards and work from there. If you dyno your engine and know the best power timing and work backward from that point, you will find most V8 engines make best power between 32deg to 38deg total timing. So when you curve your dist. you will want all your timing in at 3000rpm and your base timing should be 20degs. This will clean up the idle and make for good throttle response. But will also make the engine run cooler. With that being said you have to run ported vacuum to help the engine run cool at cruse speed. The timing at cruse may be as high as 44degs, this will help the engine run cool. But when you do step on the throttle the advance has to drop out as fast as possible so the engine does not go into detonation. Of course you do not want to be going to WOT if you are crusing along at 2200 rpm.

[@moto_rad]

Before emissions, timing was all manifold

[@billcat1840]

We always plugged in to ported vacuum for street cars. Manifold vacuum pulls your timing in too quickly. full advance at low RPM not so good. Ported vacuum allows the timing to advance for cruise conditions and really helps fuel economy.

[@ThunderHead289]

Mechanical and vacuum advance function completely independent of each other. When you punch the throttle vacuum advance timing drops out and you are only on mechanical.

[@billcat1840]

@@ThunderHead289 Yes you are correct. I was referring to total timing. I used to set up Pontiacs for Stock competitions. Ever spend any time with a Sunnen Distributor Machine? I can operate one blindfolded. Its old school black magic we practice. These kids with computers have no clue.

[@billcat1840]

We would lock out VA on a drag car. Relying on initial and centrifugal. Sometimes different conditions would dictate a slower or faster centrifugal rate. A street vehicle was smoother and had better economy when VA was correctly dialed in.We used to swap cans around to get the curve we wanted. I had a tech manual that listed the VA rates and weight numbers for various timing curves among the manufacturers. Ever set timing with a vacuum gauge? I remember telling kids that nothing they slapped on their motor was going to perform well until they got the timing right.

[@johnmccloskey8761]

Very good explanation. This has always been a question that a lot of people did not understand. You nailed it! From an "old school" Tech.

[@ThunderHead289]

That means a lot my friend 🤝

[@msubtech84]

no your both wrong

[@guillermonieri4203]

Thank you for taking the time to explain the issue. Very clear, but well above my head.

[@michaelbenardo5695]

Another problem with using manifold vacuum on a mild engine is that many, such as AMC 6s, will spit back through the carb on initial throttle.

[@feelingold2995]

Thanks for taking the time and simplifying it for us... 2 thumbs up brother...

[@ThunderHead289]

Yay. 👍 I’m glad it made sense!

[@LULU1422__]

good boy

[@WW226]

For those of u who daily drive low vacuum engines, take a look into FBO Ignition products. They make custom vacuum advance cans for Ford, Chevy and Mopar. It changed my daily driver alot. Sharp off idle launches, and improved fuel economy by 2.5 more mpg

[@perotekku]

Feel like this topic is like Zinc in oil, you'll get a million opinions on which is correct. Everybody will claim they're solution works best, but everybody's setup is different. Best to get all the knowledge you can, and apply what works best for you. Great vid, Luke!

[@ThunderHead289]

That’s why I tried to prove it through tech and demonstration. But that’s like ten years of learning I tried to put in a 15 minute video.

[@perotekku]

@@ThunderHead289 Made a post on the Facebook group trying to dispel the "ported vacuum is only for emissions", let me know what you think!

[@johnarmstrong6940]

Thanks for this great explanation. I understand this video was made 3 years ago, so might not get a response, totally understand. Im not a mechanic, but enjoy working on my car, having rebuilt the engine and many other parts. I totally understand ported and manifold and how it relates to advanced timing at Idle. I don't have a stock carb, may years ago I fitted a 44mm CV Harley Carb. It does have a vacuum port, but not a port that blocks vacuum at idle, so I have to run manifold vacuum. I have a small engine and it seems to run fine, but Ive always had in the back of my mind that Im not setting up my timing correctly. A stock spec setup should be 750RPM at idle and 10degrees on the timing. The only way I get this, is if I disconnect the vacuum, block it off, set the timing and reconnect the vacuum. But now I have 1100rpm at idle. I have driven like this for years, but i bugs me that I idle very high. So recently I added a small electronic solenoid on the vacuum line to my distributor, with a switch on my accelerator pedal. So when at idle, with no press on the pedal, the vacuum is blocked and my idle sits at 750RPM. Then when I pull off, vacuum kicks in and advances. Question, is this a dumb idea? And should I even be looking to try match stock timing settings, when I run a non stock carb. If so, without diagnostic tools, is there a way I can work out what my timing should be, to move away from the stock specs? Thanks for your time, again, great video.

[@hvacguru-Kansas]

I always appreciate your videos. You have a gift when it comes to sharing your knowledge. My 77 F250 with stock 400 2-barrel Motorcraft actually utilizes both ported and manifold vac on vacuum advance using two 3-port vacuum switches based off of coolant temperature. One switch is set for 160, the other at 225 F. Basically, when the engine is cold, vacuum advance is receiving manifold vac. When it warms up to over 160, it then switches to ported vac. If the coolant gets too hot, (over 225 F) it then switches back to manifold vac to increase idle and help cool things down. Over-Engineered? Perhaps. But I've kept it that way since I've owned the truck which is about 33 yrs. Switches still work but I discovered yesterday my vac advance canister diaphragm is leaking. I'll be needing help to get things adjusted when I figure out what advance module to install on my distributor. I'm definitely not a car guru... just an old hack still trying to figure things out.

[@chipwright6193]

That's really interesting. I never took the time to understand what all of that was for. I have a 79 F150 with the 351M.

[@hotrodray6802]

It's a smog thing.

[@slowpoke4557]

You ever want to sell that 77 then I'd sure be interested! Sounds like you've taken good care of it

[@hvacguru-Kansas]

@@slowpoke4557 One should never say never... but I never plan on selling that old thing. Costs me nothing to sit in my driveway (drive a company truck through the week) and she starts and runs like a dream.

[@KBS117]

I run manifold, and with a high lift mild durated cam.. the reason? I run my AC. The compressor will kill the engine or it will die when you drop it in gear with the AC on. If you set the base timing high enough with port vacuum, to not die, the engine kicks back during cranking. With manifold vacuum I can lower my base timing and let the manifold vacuum advance the timing at idle and smooth out the low end drivability problems, and still have the engine start without kicking back during cranking. To each his own.. and that's only on the 460 I run nothing else. I also learned a trick. Lengthen the stroke on the vacuum advance, so it advances further than stock. This way, you can run a lower base timing and allow the manifold vacuum, pull the timing higher and make up for the lower base timing. You have to modify the base plate, by elonging the grooves on it, and let your vacuum advance pull it further around. Works great..

[@karlx-1]

Precisely!!

[@mcwbadass]

Great video brother! One thing I'd like to add to that conversation is an explanation of idle air bypass and how that needs to come into play with more intake duration (and overlap) on your camshaft to facilitate that sweet spot of the butterflies (into the transfer slot before the ported vac port) at an idle.

[@davearmstrong7745]

Thank you for this video. I recently noticed that my distributor vacuum was connected to manifold vacuum. Just like you said, after moving it to ported I lost the vacuum advance that was there with the manifold connection. Idle became more rough. Now thanks to you I know to add some mechanical advance to smooth out the idle.

[@TheMikel302]

I like the custom alternator shims (washers) lol. Its cool how you proved the theory with the 2 vacuum gauges. You are pretty knowledgeable with this stuff. The carb return line was cool to see as well.

[@ThunderHead289]

I actually have since made the spacer but never installed it! I’m glad you enjoyed the video! It worked for on prototype peanut harvester machine in Virginia for a company back in 15 and we used a lot of washer shims. So I call that the “Amadas spacer” now 😂

[@22kpar1xcyberdyne9]

I'm old school. I've always ran Chevys with ported vacuum and Fords with vacuum as you increase rpms. As most people know, Chevys are tough and will easily revv 8k but weak v8 Fords are limited to 5500 rpms. Sure you can revv higher but Fords will experience valve floating on their single valve spring design. I appreciate your video and will have to put your information to a test on a stock 350 chevy next month. And I never knew what those slotted vents were on a carb. Lol. I'm open to learning old knowledge because I am not a know it all.

[@johnmilner7603]

Not all old engines had ported on their carb. For instance my 70 Z28 just has a full manifold port on the 4555 Holley.

[@ThunderHead289]

I tried to say it doesn’t work for everything - that was the factory screwing people to keep things safe. You would have good idle timing, but your initial mechanical had to be a lazy setting unfortunately.

[@leskobrandon538]

I had a California smogged out 78 gmc jimmy, factory smog/vacuum line for the dist pot had it on a manifold vacuum just below the butterflys, which added to the static timing while running.. I switched to ported vacuum and it ran tons better with better fuel economy... This was a built 4 bolt main sb 383 stroker with every California illegal internal part you could think of.. but yet it ran cleaner than a new at that time 92 honda accord, the smog guy was surprised at the sniffer results... The only California legal part I had on it was the MSD 6A and distributor/coil. Even the heads were California illegal dart 2 open chamber heads 202/1.6 with big intake runners, the pistons were trw 11.1 pop-ups but with the heads final cr was at 10.1.. no pinging after timing curve adjustment on the distr weights and adjustable vacuum pot.. lived that truck.. should have kept it.. the cam was on the higher end on the mild scale.. also did some mods to the q-jet..

[@leskobrandon538]

Every time I had to smog it, id have to swap vacuum ports and adjust timing as per the smog Nazis...

[@clemflemming9067]

When i saw your old VW in the background, I was hoping you would show one of their dual-pull vacuum cans.... Manifold vac on the back and ported on the front.

[@paulhunt1079]

Hooray! Someone else who says what I've been banging on about for years regarding the (lack of for normal driving) difference between ported and manifold, and why centrifugal and vacuum advance is highly desirable. Not mentioned is ported vacuum replicates the 'start' and 'run' lever on vintage cars that retards the timing for easier starting and advances it for running, and the subsequent change to manifold vacuum which allows the idle screws to be turned back without losing idle speed to lower idle emissions.

[@SargentRestoration]

I'll have to take a look at my truck, my old 350 i just tuned with a vaccum gauge but has a slight hesitation when I first floor it. I'm going to double check where I have my vacuum advance hooked up and adjust that idle screw. Didn't know that having it at the bottom was bad, my truck idles fine but now that I know about those little ports underneath I'll make some adjustments. Thanks! Going to double check my timing too

[@billcat1840]

If you're running a Quadrajet check yor secondary door opening. An allen wrench and a small flat blade screwdriver is needed to adjust it. Take your finger and push the door open. You should feel slight resistance. Your Secondary flapper could be too tight or loose. Both will cause a stumble. These flaps also control the secondary fuel flow. Experiment with the tightening and when you hit the right spot you'll love the Quad. I can make one run circles around a Holley..Used to build them for S/E Pontiacs.

[@jeffparris8387]

Refreshing to see a young fellow like yourself knowledgable on proper distributor operation and carb tuning. I though all you kids cared about was LS swaps and smartphones.

[@ThunderHead289]

I’m competitive and typically against what everyone else is into - get my kicks from going against the grain. Nothing pleases me more than blowing the doors off some injected peckerwoods

[@michaelbenardo5695]

@@ThunderHead289 Isn't a blast to do so?

[@jimbill6205]

I setup timing a little different. Fist, I set initial timing to highest vacuum and still able to hot start. On my 383 sbc I run 18 degrees initial. Then I worked full throttle mechanical only. My engine liked 34 total, so I limited the mechanical to add 16 degrees as fast as it would take it (18+16). Last, I used ported vacuum advance to add for no load cruising, for a total of 52 degrees (18+16+18). Idles at 750 rpm with 10 inches vacuum in gear no problem, no detonation at WOT, and cruises pleasantly smooth. Today's gas is different than in the 60s and 70s. If you run on the lean side, it actually takes longer to ignite at idle. You need to dial in air fuel ratios first then time the ignition to what the mix wants.

[@mickangio16]

Yessiree👍

[@chemgamer1419]

Thanks for the video. I have the Progression distributor. Can't live without it because I've tried so many settings and it's saved me a ton of time. I'm relatively new to the hobby so that's why I've tried so many settings. This video provided a lot of good information.

[@066motocross]

Awesome explanation. I have an 83 Chevy k10 with a 305 quadrajet. I could never really get this motor running right until I recently bought an advance timing light and set total timing at 35° it's running so much better but I installed a new HEI and I'm not sure how to set the vacuum advance. I get just a little miss barely noticable at part throttle only in 1st gear. It revs great but I think that vacuum canister needs adjusted. Man! Your video is awesome!

[@joe-hp4nk]

Fuel burns at a constant rate, the faster the engine turns the less time it get to do its job, hence advancing the timing. It's a balancing act between high compression, high octane, and piston speed. The weights in the distributor don't really start to move untill the engine gets to about 2000rpm, but the vacuume comes on almost instantly, giving the engine more timing at the get go. You can smooth out this transition by using lighter weights in the distributor.

[@ThunderHead289]

Somewhat correct - higher cylinder pressures burn faster. Lower cylinder pressures burn slower. If what you say were completely true, timing would never stop increasing, but we assume wide open or darn near at 3500 plus rpm, so we stop advancing timing by then. 3500-6000 is the same advance, because at wide open throttle, cylinder pressures are constant

[@joe-hp4nk]

@@ThunderHead289 When I mentioned high compression I was referring to compression ratio. Most engines on the planet run best at about 34-36 degrees total advance all in at about 3000 rpm. After 3000 and higher cylinder pressure, you're right, more timing is not needed due to faster burn rates. It all boils down to avoiding detonation at all cost. A blown engine is no fun.

[@gregriutzel7834]

Small disagreement here. I remember when ported vacuum came in as an emission strategy. Breathing vs advance came down to base timing plus the distributor's curve vs rpm with vacuum advance for idle and light cruise. WOT response depended on the distributor's base timing plus the advance curve to full advance. The curve could be tuned with different weights and springs to take advantage of fuels, tuning or valve timing mods in addition to base timing and carb settings. Spring/weight kits used to be on the wall right alongside carb tuning kits at the gearhead and jobber oriented auto parts shops. One benefit of advanced idling is idle temps run cooler. Your videos are fantastic, keep up the great work!!

[@jimmywilson1388]

Man I’m so glad I found this channel. It’s a gold mine! I pretty much knew about the ignition timing already but it’s always interesting to learn new tricks. That’s a nice old truck btw, I recently bought a 72 Ranger XLT.

[@douglorimer5985]

Being a Ford guy when ever I see another Ford guy having trouble I love to help.

[@LukeBrinkerhoff]

Doug Lorimer being a Chevy owner is so lonely.

[@imken2392]

You must be busy...Lol...JK sorry, it was there so I took it...

[@junker7791]

Was enjoying the video, you said goodbye and spun around in your chair - that LeMans almost made me fall out of my chair! Bravo!!

[@countrymile5745]

I dont even have mine hooked up. It is sluggish coming out of 3rd into 4th gear. So I guess I need to try this. 1983 F250 302 with a 4 speed.

[@ThunderHead289]

Hooking it up to anything is better than nothing at all! 👍

[@MatthewBerginGarage]

You will want to get it hooked up. You are wasting a lot of fuel if the vacuum advance is not operational.😰

[@samhicks97]

Roughly 5 years 5 YEARS, i've been trying to figure out why i can't get my vacuum gauge to respond while adjusting the idle mixture screws, my gauge was on ported vacuum DOH! Thanks for clearing that up Thunder, it feels surreal now that i have figured it out.

[@darthbader6506]

This is great, I'm going to have to watch it a few times to feel I've completely got it though! Thanks for sharing

[@douglorimer5985]

As a Ford guy,on my 460s and any Ford of this era. I use an adjustable vacuums advance using full man. Vac. Base timing is set. Centrifugal is set and then the vac advance is hooked to full manifold vac. And the Ford dust. Is infinatly adjustable. At my altitude with a stock 460 I run 12 basic timing,30 centrifugal.and and cruise (no load on the engine) around. A grand total of 50. Learn your centrifugal weight adjust ment ,and. Then cap off your ported. vacuum And using the original dust. With duraspark,blue chip electronic system will allow you to run cheaper better more obtainable parts. The part of the dist. That your roter rides on verys from different dist. Enabling you to establish any total timing you want. This is true with the springs also. Where I live at 6000 feet above sea level we advance for more throttle response and drivability. Good luck.

[@magdump7380]

I’ve also had good results with not running any vac advance but instead I’ve modified my mechanical advance to only allow ten degrees and then set my initial timing at around 25 for a total of 35 degrees with lighter distributor springs on my SBF.🤘

[@Gonecheenin]

I always tune my carbs/timing without the vac advance hooked up, then once it runs the best I go back & reattach an adjustable vac advance to manifold vac (always seems to have worked the best for me) & take it back out to set when & how much the vac advance does for best cruise/part throttle torque.

[@ThunderHead289]

Essentially when driving it’s all largely the same, but adding 10 plus degrees after you do all your carb idle settings is going to raise your idle rpm forcing you to go back and readjust the carb afterwards. If you actually went back and connected to ported, everything would be all equal on a vehicle that you set up as you describe

[@THRASHMETALFUNRIFFS]

@@ThunderHead289 I think you disconnect and plug it during ur mechanical adjustments to prevent that "getting into the ported draw" you described... then adjust the carb mix, then connect vacuum advance and bring idle down where you like.

[@twoeaglesgarage6223]

A video on that high idle switch would be awesome

[@KillSwitchNY]

It looked like he had an air conditioner compressor kick up solenoid hooked to the carb but wired it to on/off switch instead of the a/c. Pretty clever. You just have to buy the correct bracket for your carb. I know Holley and Edelbrock sell them 👍.

[@anthonyevich3836]

yes. I want to know how he did that.

[@georgesviderski2469]

Its called an idle stop solenoid. Stock engines had idle solenoids on there from the factory after 68, 69 approximately. Not all of them, but emissions had gotten stricter and stricter. It prevented engine run on condition , when you turn the key off. It's an anti dieseling feature. It's a electrical solenoid, one wire, it's body is the ground. AC cars had them too, because of the load the compressor added while activated.

[@KBS117]

It's just the kill solinoid screwed out. Dieseling was a big problem back in the day. The only way to kill a hot engine was to close the throttle plates completely. Ford used a electric solinoid to hold the throttle plates at idle. When you turned the key off, the solinoid retracted and closed the throttle plates, eliminating dieseling. He just wired it to a toggle switch, and adjusted the plunger out for a higher rpm. Neat trick..

[@parkdw1]

Its true that its just an a/c high idle solenoid, but which one? most will not have enough push to open the throttle on their own, they just hold the throttle open after you have pushed the gas.

[@warrenzevonsangryghost6055]

That Ford left the factory with vacuum advance connected to a port on the 4100 carb that gave it full manifold vacuum, as most engines did till about '68 or thereabouts. Ported vacuum was an emission jerry-rig to help air pumps burn more of the unbunt fuel in the exhaust manifold at idle. Engines with full vacuum to the distributor run significantly cooler at idle with considerably lower under-hood temperatures, which may be a factor for you (especially in the summer if you spend much time idling, such as in traffic). I wrote an article about ported vs manifold vac back in the late 70's for a local gearhead mag, but I cannot find a copy. Guys were buying race distributors (no vac advance) for the street and wondering why their headers & cast-iron exhaust manifolds were glowing red after idling for a spell...and wondering why their gas mileage was worse then their most pessimistic expectation for their newly rebuilt motor. Many (most?) aftermarket carbs (like Edelbrock) will have a choice of ported or manifold vac for the dist. Anyway, there's an article over at Super Chevy that goes into a bit of detail about this: tinyurl.com/yarced6e I understand the point you are trying to make about the throttle being closed so far that you may get a lean stumble off idle, but I've not experienced this with a properly set up carb and working accelerator pump in 50 years of wrenching, even when using full manifold vacuum. If ported works OK for you, then that's fine, but personally I like to keep the engine and engine compartment temps down as much as possible, so I go for full vacuum to the distributor. Anyway, love your vids Luke! Keep wrenching brother!

[@ThunderHead289]

Advance you initial mechanical and limit your total timing - then run ported. A guy can’t just run ported - the ability to advance initial mechanical is where the Benefit lies. Most timing configs are too conservative, this allows you to have a more aggressive timing curve and make much more power when hard in the throttle

[@warrenzevonsangryghost6055]

@@ThunderHead289 I guess one thing went unsaid when I mentioned that most aftermarket carbs gave a choice of ported or manifold vacuum: a LOT of OEM carbs for 60's vehicles did not give you an option (think most of the Quadrajets did, and most of the later 60's AFB's). Manifold vacuum or bust for the majority of 'em. That 4100 uses ported vacuum to the distributor IIRC, so I believe I was mistaken in my previous post. The 2bbl Rochesters and Carters used by GM and Chrysler mostly used manifold vacuum. I cannot remember one way or another about the Autolite 2100...think it might be manifold vac? Shit, I'm old. It'll happen to you too. The only 60's vehicle I own now is a '69 Jeepster with the Buick odd-fire 225. The best all-around carb for this motor is the lowly Rochester 2GC (bulletproof little bastid). Manifold vacuum only. Tune-up specs call for 5° initial and specs for the Delco distributor say an additional 22° or so with mechanical and 16° more for the vacuum adv. I add a few degree to the initial before it starts getting pissy with fuel. Also might note that lots of initial advance can make the car a PITA to start on winter days. So, not everyone has a choice of vacuum ports, and not everyone is trying to turn their rig into a 1/4-mile beast, so as long as it doesn't stumble at the stoplight or passing lane, we're cool. Sometimes we're just trying to get the stock setup working as well as humanly possible.The original engineers (who knew what they were doing) gave you tune-up specs, and while they can be a bit conservative, they also had to allow for all the crappy fuel that owners might encounter (memories of the [estimated] 70 octane fuel purchased in northern Nevada circa 1972). But, if followed, those OEM specs still result in a pretty decent running motor, with no surprises. Now...if I had my old '66 Mustang K-code Fastback again (sigh😢) and was gonna pop on a new AVS2 or Street Avenger (both great carbs), I'd go for lots of initial + ported vac, with an adjustable vacuum canister to limit total adv. 👍 If I didn't apologize before for this lengthy tangent, I'll do so now. Most of your target audience is looking for performance advice with aftermarket upgrades., and you are spot on in these cases. Suppose I jumped in for the guy with an old carb looking for the *missing* timed vacuum port.🤷‍♂️

[@nathanmccree3089]

Thanks for sharing your knowledge Luke great video like always Luke 👍

[@daviddixon798]

Thank you finally someone who knows what he's talking about I have a much better understanding of vacuum advance now

[@ddgatewood71]

That helped fill in a few blanks. Hopefully I can remember it :)

[@kennethjennings9292]

Man, the exhaust on that truck sounds freaking awsome!

[@ThunderHead289]

It’s just long tubes and glass packs with some flex pipe 😅

[@kennethjennings9292]

Sometime the homemade stuff just works in the right combinations, i.e. your truck lol

[@wyattshelton2080]

I miss my 66 chevelle, seeing the dash in the end clip of the tunable dizzy made me sad lol

[@charlievanness3651]

I have come across a lot of older cars where the carburetor has been rebuilt or changed to a Holly or Eldabrock and the person doing it had hooked up the vacuum advance wrong then came to me complaing about the way there car runs and performs. Hopefully a lot of people will watch this video and pay attention on where to hook up there vacuum lines.

[@jocrp6]

Use manifold vacuum when you have too much compression and cannot even reach standard ign timing while starting.

[@ThunderHead289]

Or instead of sacrificing performance, put your ignition on a toggle switch and once the engine is spinning, flip it.

[@Wrktrk]

@@ThunderHead289 I liked your video. let me possibly give you another viewpoint. on a mild to performance STREET engine vacuum advance is worth 2-3 mpg . how i do this is , With vac. adv. u hooked. I Set the distributor up for best preference. I like to use an adjustable vac. adv.can.( but you can modify a stock easy enough. ).plug in the vac. adv to manifold vac. re-adjust idle speed & mixture. now the engine doesn't care whether you have 1 person or 5 empty or full load. I do this with a 406 powered S10 . it doesn't care whether I am making a pass at the track, rolling down the Hwy getting 17mpg or pulling a trailer with a tractor. I have setup all of my vehicles this way with good results and reliability .

[@mjmcomputers]

I normally stick with manifold vacuum but good to see your explanation on which is best based on camshaft.

[@ThunderHead289]

It’s one of those odd things - stock and mild cams just take so much less timing at idle to the point that hooking manifold vacuum up causes a guy to have to run very little initial mechanical for an overall idle timing number to not be way excessive

[@jtthill5475]

And that is why it is called Vacuum ADVANCE. Ported rules.

[@billbirch3748]

Tried it both ways, ported and manifold after getting into a discussion on it just to prove to myself. Did the test both ways with a stock 350 and a streetable healthy 406. Ported worked best for both engines regarding drivability and seat of the pants feel throttle response. I did not use a dyno just common sense and which felt better. Looking at getting a complete 400ci Blueprint engine with carb and HEI as you can't build that power for the price and the warranty. They don't use vacuum advance at all. Run initial of 15º which is high. No stock starter motor likes that. Full in 34-36º by 3500. About 20º mechanical advance and you are right. Who knows what the advance curve unless you tested it? Holley's dizzy that goes with the Sniper EFI system has a near vertical advance curve off idle then flattens off abruptly. Engines do not run at 250k baud rate so that all needs massaged. Since BP designs and dynos every engine, I believe they tailored the best mechanical advance curve with weights and springs for every engine they offer. Maybe it's not perfect to the degree at any given RPM under any load but close enough. Timing is everything regarding power. Good video. Thank you

[@robewalk2]

Luke, I can see why you like the older vehicles compared to newer ones. A person can actually work on the older engines and get results. Good content. And the Volkswagen in the background, what year is it and is it one of your fleet? It looks sweet. I hope you and yours are healthy and safe and look forward to your next episode. Cheers from Tennessee.👍😷🍻

[@ThunderHead289]

It’s a 67 and it sure is mine - it’s probably my most neglected project! I got it for a song, but Iv been so busy I just haven’t gotten to it!!!

[@cravinbob]

Yeah, the bumper and turn signal on top of fender say mid sixties. Earlier had small bumpers and later years the bumper changed totally.

[@jeremiahsmith6689]

when i was playing with the frankensteined 302 form an 80 f150 that's in my 67 mustang i didn't touch the mechanical timing but switched it back and forth to see what i noticed manifold vacuum gave me more acceleration but i used gas a lot faster

[@ThunderHead289]

It actually shouldn’t matter - the only reason you noticed an improvement with manifold is that your idle settings were done up for manifold. So with everything out of wack and loaded up on ported, it’s no surprise it struggled off the line. But if you run ported with mechanical advanced, you will have a much more effective mechanical timing curve. Like I say in the video- you can’t just flip back and forth without doing anything else and make a determination based on that

[@jeremiahsmith6689]

@@ThunderHead289 MY understanding had improved after that day.I use ported. I didn't know how to properly set the gap on the points. i upgraded to pertronix II thatr lasted roughly 3 years now im back on points $8 vs $120 . I haven' t grasped checking my dwell quite yet

[@arcorob]

This was great...I understood this (because I have followed you) but you cant get any clearer than this video..One comment...Dude..If you add any more gauges or switches you will need a 220 Amp Breaker box...LOL

[@ThunderHead289]

Iv been meaning to make this video for a long time!!! Now I can FINALLY take that second vacuum gauge out!!!

[@swampy6x659]

Vacuum at idle is available with automatic trans in some GM vehicles . [The same model runs ported on manual g/box . ] Re manifold vac,, xtra advance I assume would help pull thru the convertor stall on the auto . Tune up for auto was pull vac line and plug then set base timing .then reconnect.

[@markthor7865]

Awesome video Luke! Fantastic explanation of the two vacuum advance types. Love it 👍🏻👍🏻👍🏻

[@ThunderHead289]

Thanks so much! There were some thing I could have done better for sure, but I’m glad it made sense!!!

[@quirinonavarro1857]

This is the most accurate and understandable explanation of this subject. Whit an excellent presentation. Congratulations!! Saludos!

[@jakebullet8990]

Ported vacuum?? What kind of Voodoo is going on here? Joking aside, My 65 Barracuda likes ported but my 67 Tempest likes manifold.

[@ty2010]

I had different motivations when setting up delivery trucks , ported will carbon load a lot more with a lot of idle time but manifold will make it run hotter at idle. Ported will allow a bit better tweaking to get mileage pickup when running empty on the highway without risking predet when under load It does get complicated when the goals are changed.

[@fredtflail]

You use ported vacuum. Plain and simple

[@jrobpat0154]

exactly ! trying to get a cold engine to start and run with manifold vacuum is a pain

[@gergatron7000]

I'd like to add that running manifold vac advance can cause another problem: when accelerating from high vac to low, the vac advance cannister is delayed in its return to base timing, causing a split second of ignition knock as the accelerator is applied. In my experience, it otherwise made a big difference to cruise and idle performance. My fix was to fit MSD programmable, the timing response to load (via a MAP sensor) was then instant. I am running approx 35 degrees timing at idle on a 302 Cleveland, up over 40 at cruise.

[@53_ford_custom15]

I’m 14. I have a 53 ford customline that I am building into a ewrly 60s style custom. I just built up the old flathead and stroked it an all thag good stuff. I work at a machine shop to make the money for my build. I’m the only one in my family into this stuff. And I just did all this to my motor. And this is what I figured out. As of now I have my distributor set up on manifold vaccum because I can put as much timing into the distributor as I can before it kicks back. And then once it fires it gets even more timing from the manifold vaccum at idle. But if I did this at the port I would have less timing at idle and therefore less total timing.

[@ThunderHead289]

When you mash the pedal, you lose your vacuum advance timing. So by moving to a lesser mechanical unit I’ll setting, you are leaving power on the table - this is what a lot of folks end up doing.

[@53_ford_custom15]

ThunderHead289 so it’s only advanced at idle? And when you gain rpm you loose vaccume, therefore you loose advance?

[@ThunderHead289]

53_Ford_ Custom vacuum more so relates to your throttle position. Run a vacuum gauge into your cab and step on the throttle and observe the gauge - vacuum will drop. When this happens, you also lose vacuum advance where you are strictly on your mechanical timing. Pretty cool a guy your age is into this stuff - check out the ignition timing playlist on my channel page, it will be very helpful for understanding ignition timing!

[@53_ford_custom15]

ThunderHead289 got jt! Thank you very much!

[@michaelbenardo5695]

You set up timing with the vacuum advance disconnected. AFTER you set the timing, you re-connect it. Remember, your stock distributor only had a vacuum advance, no mechanical advance, so you must use ported vacuum, or else you will have no spark advance. It will run at full advance most of the time, which will cause severe pinging under load, and way too much advance at idle. It might be impossible to start that way or break the nose off of the starter. You must go to an aftermarket distributor with both mechanical advance and vacuum advance if you want to experiment with ported vs manifold vacuum.

[@mean_sbc8653]

I have a Chevy performance crate 350 and I got the beefed up one with the cam and some other things but I’ve set the initial timing to what the build sheet says to and I can never get it to run decent on ported at idle it sounds like garbage but whenever I run it at full it sounds better and it seems like better off idle throttle response. But every engine is different this is what I see to be the case with mine

[@ThunderHead289]

It’s because you need more mechanical initial timing! 👍 I basically go up to 16 or 18 advance, then if it needs more I’ll open the throttle 1/8th turn and then drop down the initial timing. This is all a balancing act - now really big cams are going to favor full manifold vacuum. I can get into why, but that almost needs a video all it’s own!

[@mean_sbc8653]

ThunderHead289 if only the vaccum advance wasn’t hitting the intake 😂 I could fix it but I’m lazy and but yeah right now it’s as advanced as it’s gonna get as far as initial

[@mitchellferre1652]

I knew the do and don'ts but didn't know why. I was taught to disconnect vacuum advance and rely on mechanical advance with springs in distributor. But we were always running huge cams. I run 33 degrees total timing on my 440 Chrysler, all in by 2500rpm. 248 duration cam @.050. 3000rpm converter with 3.91 rear gears and it doesn't see much low rpm operating.

[@cesareomendez6794]

I have the same cam specs and 3.91's out back. Mine is a 360 smallblock mopar. However, in upper rpm engine seems too want to layover or lose some power not sure why?🤔

[@mitchellferre1652]

@@cesareomendez6794 yes my 440 has been doing the same thing for while. I ruled out the timing and ignition system after it checked out ok. My secondaries may not have been opening. Replace the accelerator pump and secondary vacuum actuator. Also going to try a 750 mechanical secondary carb. I'm thinking it may be worn valve springs. I won't know till spring

[@TheSteelArmadillo]

Thank you for making this video! You talked me through a problem I’ve been having for over a year on my 351w and it’s running better than it has since I rebuilt it.

[@tomstulc9143]

Look I grew up on in the sixties and seventies we was taught in auto shop and in the motors manuels to set timing with the vacume advance and the hose plugged. It was straight forward. Set initials timing and max timing then reconnect the vac advance.

[@movingearthmusic1893]

I had an old Cadillac that had a thermostatic vacuum switch that would run ported vacuum to the advance until a certain temperature was reached then it would switch to manifold. Kinda like a high idle setting.

[@michaelbenardo5695]

When the water temp passed a certain point, it would switch to manifold vacuum to raise idle speed and give cooler running.